Photochromic spectacles are the spectacles which, when used outdoors where they are irradiated with light containing ultraviolet rays like sunlight, are quickly colored and work as sunglasses and, when used indoors where they are not irradiated with light, fade colors and work as ordinary transparent spectacles. In recent years, in particular, the photochromic spectacles using photochromic plastic lenses are finding ever increasing demands.
The methods of producing plastic lenses having photochromic properties can be roughly classified into the following three methods (in the following description, ordinary lenses without photochromic properties are simply called lens materials).
(i) A method of directly obtaining photochromic lenses by dissolving a photochromic compound in a monomer to polymerize it (in mass method).
(ii) A method of forming a photochromic layer on the surfaces by imbibing a lens material with a composition containing a photochromic compound (imbibition method).
(iii) A method of forming a photochromic layer on the surfaces by coating the surfaces of the lens material with a composition (photochromic coating agent) in which a photochromic compound is dispersed (coating method).
Among the above methods, the mass method has a limitation in that a special monomer composition must be used for expressing good photochromic properties. According to the imbibition method, the lens material must be so soft that the photochromic compound diffuses therein. In contrast with the above methods, the coating method offers an advantage in that photochromic properties can in principle be imparted to any lens materials, and is drawing particular attention in recent years.
Though the coating method is accompanied by a serious technical problem of firmly adhering the photochromic layer on the lens material, there has now been developed a coating agent capable of forming, on the lens material, a photochromic layer having a highly adhering property and its practical use is becoming a reality. For example, patent document 1 proposes “a curable composition comprising a radically polymerizable monomer having a silanol group or a group capable of forming a silanol group upon the hydrolysis; an amine compound; and a photochromic compound, each in particular amounts” which is used as the above photochromic coating agent.
As described above, the coating method may be a very excellent method of producing photochromic lenses. However, when the lenses having a photochromic layer formed by the coating method are used for extended periods of time, a problem arouses in that a photochromic compound in the photochromic layer is deteriorated to lose color density or turns into yellow causing the lenses to appear in yellow color even in a state of not developing color (even in a state of not being irradiated with ultraviolet rays). In particular, when an indenonaphthopyran compound having good photochromic property is used as a photochromic compound, the deterioration becomes conspicuous. The above problem similarly occurs even with the lenses having a photochromic layer formed thereon by the imbibition method. The main cause of deterioration of the photochromic compound stems from that the photochromic compound comes in contact with oxygen in the atmosphere and is deteriorated by oxidation.
As a method of preventing the photochromic compound in the photochromic layer from being deteriorated by oxidation, patent document 2 proposes forming a thin layer of metal oxide particles or fine metal particles on the surface of the photochromic layer having a thickness of about 20 μm.    Patent document 1: Leaflet of International Laid-Open No. 03/011967    Patent document 2: JP-A-6-192651